[20.03] Photospheric Motions and CME Productivity

Shearing motions have been frequently used in MHD
simulations of CME initiation but have hardly been reported
from observations of CME--producing regions. In this paper
we investigate whether the bulk of magnetic helicity carried
away from the Sun by CMEs comes from helicity injected to
the corona by such motions or by emerging magnetic flux. We
use photospheric magnetic field observations of active
region NOAA 9165 which is an ideal candidate for such study
because (1) it is the site of both new flux emergence and
intense horizontal shearing flows; (2) it shows rapid
development and rapid decay and for a few days it is the
site of violent activity; (3) the horizontal motions occur
when it is close to disk center, thus minimizing the errors
involved in the relevant computations; (4) observations of a
magnetic cloud associated with one of the CMEs linked to the
active region are available. The computed helicity change
due to horizontal shearing motions is probably the largest
ever reported; it amounts to about the total helicity that
the active region's differential rotation would have
injected within 3 solar rotations. But the CMEs linked to
the active region remove at least a factor of 4--64 more
helicity than the helicity injected by horizontal shearing
motions. Consequently the main source of the helicity
carried away by the CMEs is the new magnetic flux that
emerges twisted from the convective zone. Our study implies
that shearing motions, even when they are strong, have
little effect in the process of buildup of magnetic free
energy that leads to the initiation of CMEs.

The author(s) of this abstract have provided an email address
for comments about the abstract:
anindos@cc.uoi.gr